Arthropod Diversity Flashcards
Arthropod anatomy
- Externally and internally segmented
- Jointed appendages
- Well developed exoskeleton
- Tagmosis - head and trunk
- Headshield (carapace) often present
- Complex association of compound eyes
- Open circulatory system: haemocoel
- Dorsal heart and pericardium (membrane enclosing the heart)
- Ventral nerve cord
Segmentation of arthropods
Body divided into repeating units
Limbs similarly subdivided
Arthropod exoskeleton
- Made of chitin
- Harder in some areas than others where there is a need for rigidity or elasticity
Advantages of exoskeleton
Protection and prevents desiccation
Disadvantages of exoskeleton
Limits to size, and moulting makes arthropods very vulnerable
Features of Arthropod moulting
- Regular shedding of external cuticle
- Facilitates the need to grow
- Arthropods delicate at this time
- Initially epidermis separates from cuticle
- A fluid is then secreted between the epidermis and the cuticle, and the epidermis grows
- A new cuticle begins to be secreted by the epidermis
- Enzymes are then secreted in the moulting fluid, causing the shedding of the old cuticle
Arthropod legs
- Either biramous (dividing into 2 branches) or uniramous
- They serve a large range of functions
Arthropod Hox genes
Transcription factors involved with anterior-posterior patterning, primarily
Play a role in segment identity
Third maxilliped in lobsters made from a mixture of the expression of UBX and Abd-A
Internal Arthropod anatomy
- J-shaped gut
- Ventral nerve cord
- Dorsal heart pericardium complex
Arthropod eyes
- Compound eyes are made up of many individual photoreceptors which are receiving light and creating an image
- Camera eyes found in jumping spiders. They possess a cornea which focuses light onto receptors
Onchyophorans
- ‘Claw-bearers’ / velvet worms
- Terrestrial worms with soft cuticle
- Stubby animated worms with telescopic claws
- Set of oral papillae (small round protuberance) that secrete slime for predation and mandibles
Tardigrades
- Moss piglet or water bearers
- Marine and terrestrial
- Stubby, claw-bearing legs, usually 4 pairs
- Triadate pharynx (splits into 3)
- Eutelic (fixed number of adult cells)
- Stylet apparatus (spines to pierce tissues)
Trilobites
- 530-250 million years ago
- Had calcimine cuticle so preserve easily
- They had spines to protect them from predators
- Possessed well-developed eyes
Anomalocarids
- Top predators in the Cambrian period
- Around 1 meter long
- Specimens had delicate spines with bristles along them, designed for suspension feeding
- Others had mouths
Opabinia
Eyes on stalks
Single appendage on trunk with claw
